Mechanisms of Methane Hydrate Formation in Geological Systems

Abstract

Natural gas hydrate is ice‐like mixture of gas (mostly methane) and water that is widely found in sediments along the world's continental margins and within and beneath permafrost and glaciers in a near‐surface depth interval where the pressure is sufficiently high and temperature sufficiently low for gas hydrate to be stable. We categorize the myriad of geological gas hydrate deposits into five characteristic types. We then review the multiple quantitative models that have proposed to describe the genesis of these deposits and describe how each may have formed. We emphasize the importance of coupling multiphase flow (free gas and liquid water) and multicomponent reactive transport with geological history to describe the dynamical processes of gas hydrate formation and evolution in geological systems. A better insight into the kinetics of methane formation from microbial biogenesis and the processes of multiphase flow at the pore scale will advance our knowledge of how these systems form. By understanding the generation and evolution of gas hydrate through time, we will better decipher the role of gas hydrate in the carbon cycle, its potential to contribute to climate change and geohazards, and how to design optimal strategies for gas production from hydrate reservoirs.

Fluid Accumulation, Migration and Anaerobic Oxidation of Methane Along a Major Splay Fault at the Hikurangi Subduction Margin (New Zealand): A Magnetic Approach

“…Site U1518 lies within the hydrate stability zone, and widespread but cm‐thick hydrate accumulations identified within sand‐ and silt‐rich layers led to the conclusion that the vertical flux of methane is largely controlled by diffusive migration (Cook et al., 2020). Gas hydrate formation is a slow and exothermic process that depends on temperature, pressure, methane concentration and solubility in existing pore‐water, and geometry of the pore‐space available (Collett et al., 2019; Ruppel & Waite, 2020; You et al., 2019). The diffusive transport of methane probably results in its accumulation in brittle, more porous structures within the damage zone of the Pāpaku fault from where it is more favorable to travel in a fault parallel direction.…”

Magnetic Mineral Diagenesis in a Newly Discovered Active Cold Seep Site in the Bay of Bengal

“…At site Stn-9, fracture-controlled fluid transport supported the formation of gas hydrates (distributed and massive-type) (Mazumdar et al, 2019). We believe that hydrate crystallizes within the fault/fractures zone as methane gas migrate through GHSZ (You et al, 2019). It is interesting to note that several layers of hard authigenic carbonates are found above and within the proposed distributed-type gas hydrate bearing intervals (G1, G2, G2) ( Table 1).…”

“…The opening/ closing of fault/fractures due to neo-tectonic activities allowed migration of methane from deep-seated gas reservoir (Dewangan et al, 2011;Sriram et al, 2013;Dewangan et al, 2020;Mazumdar et al, 2019). Upon entering the shallow depths and encountering conducive P-T conditions, gas hydrates started crystallizing within the faults and fractures where methane concentration exceeded the solubility limit (You et al, 2019). We propose that the distributed-type gas hydrate formed in veins during periods of reduced methane flux at clay rich intervals (G1, G2, G3) arrested the pyritization process and favored the preservation of the intermediate iron sulfides minerals (greigite/pyrrhotite) (Larrasoaña et al, 2007).…”

Gas‐Driven Tensile Fracturing in Shallow Marine Sediments

“…Particular interest has been given to hydrate that occurs as a filling in fractures and veins (Cook & Goldberg, 2008; Cook et al., 2008, 2014; Daigle & Dugan, 2010b, 2011; Jin et al., 2015; Nimblett & Ruppel, 2003). These features tend to occur predominantly in clay‐rich sediments, suggesting that they are related to low permeability and associated elevated fluid pressures (Daigle & Dugan, 2010b, 2011; Ginsburg & Soloviev, 1997; Sassen et al., 2001; Weinberger & Brown, 2006), or that they form as a result of capillary forces inhibiting nucleation of disseminated hydrate within the pore space (Clennell et al., 1999; Cook et al., 2014; Rempel, 2011; You et al., 2019). The prospect that marine sediments may fail in tension or shear due to pore pressures associated with fluid flow and methane hydrate dissociation has significant implications for hydrates as a geohazard and release of methane to the water column.…”